1. Field of the Invention
The present invention relates to an image-bearing member protecting agent for protecting the surface of an image bearing member, a method of applying the image-bearing member protecting agent, a protective layer forming device provided with the image-bearing member protecting agent, an image forming method using the image-bearing member protecting agent, a process cartridge provided with the protective layer forming device, a complex machine provided with the protective layer forming device or the process cartridge, and an image forming apparatus such as a complex machine provided with at least one of a printer, a facsimile and a plotter.
2. Description of the Related Art
Conventionally, in image formation based on an electrophotographic process, an electrostatically charged latent image, i.e., a latent electrostatic image, is formed on an image bearing member formed, for example, of a photoconductive material, and charged toner particles are attached to the latent electrostatic image to form a visible image. The visible image formed of toner is finally transferred onto a transfer medium such as paper, and then fixed on the transfer medium under application of heat, pressure, gas emitted from a solvent, and the like, thereby becoming an output image.
The image forming methods are broadly divided into a so-called two-component developing method in which toner particles and carrier particles are stirred and mixed so as to be frictionally charged as a method of charging the toner particles to form a visible image; and a so-called one-component (single-component) developing method in which a charge is applied to only toner particles, without using carrier particles.
Further, one-component developing methods are classified into a magnetic one-component developing method and a non-magnetic one-component developing method, depending on whether a magnetic force is used to keep toner particles held to a surface of a developing roller.
In image forming apparatuses, such as copiers, complex machines based on the copiers, and the like for which high-speed processability and image reproducibility are required, the two-component developing methods have been employed in many cases due to demands for stable chargeability, of toner particles, stable charge rising properties of the toner particles, long-term stability of image quality, and the like; whereas in compact printers, facsimiles, etc. for which space saving, cost reduction and the like are required, the one-component developing methods have been employed in many cases.
Also, nowadays in particular, the technology of colorization of output images is progressing, and demands for improvement of image quality and stabilization of image quality are increasing like never before.
For the improvement of image quality, toners have been made smaller in average particle diameter, and particles of the toners have been made rounder in shape with their angular parts removed.
Generally, in an image forming apparatus which operates in accordance with any such electrophotographic image forming method, regardless of which developing method is employed, a drum-shaped or belt-shaped image bearing member (typified by a photoconductor) is uniformly charged while being rotated, a latent image pattern is formed on the image bearing member by laser light or the like, and the developing unit creates a visible toner image from the latent image pattern and transfers the toner image onto a recording medium.
After the toner image has been transferred onto the recording medium, untransferred toner components remain on the image bearing member. If such residues are directly conveyed to a region for the charging step, it often hinders the image bearing member from being uniformly charged; accordingly, the toner components, etc. remaining on the image bearing member are generally removed by a cleaning step by a cleaning unit after the transfer step, thereby bringing the surface of the image bearing member into a clean enough state, and then charging is carried out.
Thus, there are various types of physical stress and electrical stress in each step in image formation, which deteriorate the image bearing member, charging member and cleaning member.
In attempts to solve this problem, a number of proposals for lubricants and methods of supplying lubricating components and forming films of lubricating components have been made thus far to reduce deterioration of the image bearing member, charging member and cleaning member.
For example, Japanese Patent Application Publication (JP-B) No. 51-22380 proposes a method of forming a lubricant film on a photoconductor surface by supplying the photoconductor surface with a solid lubricant composed mainly of zinc stearate in order to lengthen the lifespan of photoconductors and cleaning blades. This makes it possible to reduce abrasion of the photoconductor surface and thus lengthen the lifetime of the photoconductor.
Japanese Patent Application Laid-Open (JP-A) No. 2001-305907 proposes a lubricant supplying device as a specific solid lubricant coating method. The lubricant supplying device described in JP-A No. 2001-305907 is provided with a brush roller (a supplying member) which is in contact with a bar-shaped solid lubricant and abrades the solid lubricant so as to supply the scraped fine powder lubricant to a photoconductor belt or an intermediate transfer belt (an object to which the lubricant is supplied).
The solid lubricant is held on a lubricant holding member with which a spring (a spring biasing unit) is contacted. The solid lubricant is pressed toward the brush roller by the biasing force of the lubricant holding member. When the brush roller is driven to rotate, the solid lubricant contacting therewith is abraded, and thus scraped. The lubricant attached on the brush roller is applied onto a surface of the photoconductor belt or intermediate transfer belt.
Further, the lubricant supplying device also includes a lubricant leveling blade. The lubricant leveling blade is provided for spreading the lubricant applied to the photoconductor belt or intermediate transfer belt to form a lubricant layer uniform in thickness thereon.
However, in the configuration where a solid lubricant is pressed against a brush roller with being in contact with a spring, the spring is extended as the solid lubricant is scraped off, and thus the pressing force naturally weakens. As a result, the amount of the solid lubricant scraped is reduced, and the amount of the solid lubricant supplied to a photoconductor or an intermediate transfer belt is also reduced. Therefore, it is impossible to sufficiently protect the photoconductor or intermediate transfer belt.
In an attempt to solve these problems, Japanese Patent Application Laid-Open (JP-A) No. 2007-293240 describes a method in which a movable pressing member is provided in a solid lubricant holding member, and the movable pressing member is pressed against a solid lubricant with a spring member, so that a constant pressing force can be maintained at the solid lubricant as the solid lubricant is scraped off from time to time.
However, it is known that with use of a solid lubricant block obtained by compression molding, it is impossible to prevent a reduction in consumption amount of the solid lubricant block over time even when a constant pressing force is maintained over a period of time (this case will be described hereinbelow in Comparative Examples).
In order to solve this problem, Japanese Patent Application Laid-Open (JP-A) No. 2007-65100 describes that the hardness of the front side of a solid lubricant in its front surface/back surface direction is made higher than that of the back side thereof, so that a reduction in consumption amount of a solid lubricant can be prevented.
However, in the proposal disclosed in JP-A No. 2007-65100, there is no description regarding a method for obtaining a solid lubricant block whose front side and back side are different in hardness.
In addition, JP-A No. 2007-65100 describes that a plurality of solid lubricant blocks having a different hardness are used in a stacked structure, however, there is no description regarding a method for obtaining a solid lubricant which is composed of a same material and has different hardnesses in different regions thereof. If the hardness of the solid lubricant is changed by changing the composition thereof, the quality of application of the solid lubricant cannot be maintained at the same level over a long period of time.
Even when solid lubricant blocks, which are composed of the same material and have a different hardness, are obtained and used in a stacked structure, inflection points of consumption amount of the solid lubricant appear at boundaries between the blocks, and thus the quality of application of the solid lubricant cannot be maintained at the same level over a long period of time in this case as well.
Meanwhile, it is understood that fatty acid metal salts such as zinc stearate, as seen in Japanese Patent Application Publication (JP-B) No. 51-22380, Japanese Patent Application Laid-Open (JP-A) Nos. 2001-305907, 2007-293240, and 2007-65100, lose their lubricating properties at an early stage due to electric discharge performed in the vicinity of the image bearing member in a charging step.
Consequently, the lubricating properties of the cleaning blade and the image bearing member are impaired, and toner particles pass through therebetween (toner leakage), and thus defective images are formed.